def describe_pet(pet_name, pet_age=1):
    print(f"\nI have a {pet_name}.")
    print(f"My {pet_name} is {pet_age} years old.")
# 一个名为Jack的小狗
describe_pet('Jack')
describe_pet(pet_name='Jack')
# 一个名为Marry的猫咪
describe_pet(pet_name='Marry', pet_age=2)
describe_pet('Jack', 2)
describe_pet(pet_age=2, pet_name='Jack')